On Wed, 06 Dec 2017 18:25:55 +0100 gregkh@linuxfoundation.org wrote:

This is a note to let you know that I've just added the patch titled

kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

this depends on commit 7e42776d5ed1f ("rcu: Drive TASKS_RCU directly off of PREEMPT")

So, pull above commit too, for 4.14 and 4.9. But I'm not sure TASKS_RCU is introduced on 3.18.

Thank you,

From foo@baz Wed Dec 6 18:04:41 CET 2017 From: Masami Hiramatsu mhiramat@kernel.org Date: Fri, 20 Oct 2017 08:43:39 +0900 Subject: kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y

From: Masami Hiramatsu mhiramat@kernel.org

[ Upstream commit a30b85df7d599f626973e9cd3056fe755bd778e0 ]

We want to wait for all potentially preempted kprobes trampoline execution to have completed. This guarantees that any freed trampoline memory is not in use by any task in the system anymore. synchronize_rcu_tasks() gives such a guarantee, so use it.

Also, this guarantees to wait for all potentially preempted tasks on the instructions which will be replaced with a jump.

Since this becomes a problem only when CONFIG_PREEMPT=y, enable CONFIG_TASKS_RCU=y for synchronize_rcu_tasks() in that case.

Signed-off-by: Masami Hiramatsu mhiramat@kernel.org Acked-by: Paul E. McKenney paulmck@linux.vnet.ibm.com Cc: Ananth N Mavinakayanahalli ananth@linux.vnet.ibm.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Naveen N . Rao naveen.n.rao@linux.vnet.ibm.com Cc: Paul E . McKenney paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Steven Rostedt rostedt@goodmis.org Cc: Thomas Gleixner tglx@linutronix.de Link: http://lkml.kernel.org/r/150845661962.5443.17724352636247312231.stgit@devbox Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

---

arch/Kconfig | 2 +- kernel/kprobes.c | 14 ++++++++------ 2 files changed, 9 insertions(+), 7 deletions(-)

--- a/arch/Kconfig +++ b/arch/Kconfig @@ -91,7 +91,7 @@ config STATIC_KEYS_SELFTEST config OPTPROBES def_bool y depends on KPROBES && HAVE_OPTPROBES

• depends on !PREEMPT

• select TASKS_RCU if PREEMPT

config KPROBES_ON_FTRACE def_bool y --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -573,13 +573,15 @@ static void kprobe_optimizer(struct work do_unoptimize_kprobes(); /*

• * Step 2: Wait for quiesence period to ensure all running interrupts
  

• * are done. Because optprobe may modify multiple instructions
  

• * there is a chance that Nth instruction is interrupted. In that
  

• * case, running interrupt can return to 2nd-Nth byte of jump
  

• * instruction. This wait is for avoiding it.
  

• * Step 2: Wait for quiesence period to ensure all potentially
  

• * preempted tasks to have normally scheduled. Because optprobe
  

• * may modify multiple instructions, there is a chance that Nth
  

• * instruction is preempted. In that case, such tasks can return
  

• * to 2nd-Nth byte of jump instruction. This wait is for avoiding it.
  

• * Note that on non-preemptive kernel, this is transparently converted
  

• * to synchronoze_sched() to wait for all interrupts to have completed.
  

  */

• synchronize_sched();

• synchronize_rcu_tasks();

/* Step 3: Optimize kprobes after quiesence period */ do_optimize_kprobes();

Patches currently in stable-queue which might be from mhiramat@kernel.org are

queue-4.14/kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch queue-4.14/kprobes-x86-disable-preemption-in-ftrace-based-jprobes.patch